This proposal is concerned with skeletal muscle function, energy metabolism and biochemical adaptations induced by exercise training. Particular interest is given to the response of the different skeletal muscle fiber types, since each fiber is characterized by distinct biochemical and physiological properties. A major alteration induced in skeletal muscle is an approximate 100% increase in the capacity for ATP provision via oxidative metabolism. We will investigate the cellular basis for this response and the training factors that influence the magnitude of the adaptation. Since we have previously found that the increased cytochrome c content (a mitochondrial cristae marker) is due to an increase in its synthesis rate, we will investigate the influence of exercise on heme biosynthesis. The response of the rate-limiting enzyme of this pathway, delta-aminolevulinate synthetase, should provide a specific cellular event that is sensitive to an acute bout of exercise. In addition, we will evaluate the consequences of purine nucleotide metabolism (AMP, IMP) during muscle contraction and the resultant influence it may have on energy metabolism. Differences probably exist between the different fiber types; furthermore, training may alter the functional capacity of AMP-deaminase in fast-contracting red muscle. The involvement of certain amino acids in energy metabolism during muscle contraction will be evaluated by following the shift in amino groups during the onset of contractile performance in situ, and by determining the extent of branched chain amino acid oxidation with a more prolonged contraction sequence. Investigations with muscle stimulated in vitro will be undertaken to explore the physiological significance of the biochemical changes induced by endurance training in the absence of the cardiovascular system. These studies are intended to expand our understanding of the different skeletal muscle fiber types and the adaptations induced by exercise training.